[PATCHv2 10/10] KVM: s390: change ipte lock from barrier to READ_ONCE

[Christian Borntraeger]

Now that we have the READ_ONCE solution, we can change the ipte lock
from a barrier solution to READ_ONCE. The barrier and the explanation
of the bug was introduced in commit 1365039d0cb3 ("KVM: s390: Fix
ipte locking")

Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
 arch/s390/kvm/gaccess.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 6dc0ad9..8f195fa 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -229,12 +229,10 @@ static void ipte_lock_simple(struct kvm_vcpu *vcpu)
 		goto out;
 	ic = &vcpu->kvm->arch.sca->ipte_control;
 	do {
-		old = *ic;
-		barrier();
+		old = READ_ONCE(*ic);
 		while (old.k) {
 			cond_resched();
-			old = *ic;
-			barrier();
+			old = READ_ONCE(*ic);
 		}
 		new = old;
 		new.k = 1;
@@ -253,8 +251,7 @@ static void ipte_unlock_simple(struct kvm_vcpu *vcpu)
 		goto out;
 	ic = &vcpu->kvm->arch.sca->ipte_control;
 	do {
-		old = *ic;
-		barrier();
+		old = READ_ONCE(*ic);
 		new = old;
 		new.k = 0;
 	} while (cmpxchg(&ic->val, old.val, new.val) != old.val);
@@ -269,12 +266,10 @@ static void ipte_lock_siif(struct kvm_vcpu *vcpu)
 
 	ic = &vcpu->kvm->arch.sca->ipte_control;
 	do {
-		old = *ic;
-		barrier();
+		old = READ_ONCE(*ic);
 		while (old.kg) {
 			cond_resched();
-			old = *ic;
-			barrier();
+			old = READ_ONCE(*ic);
 		}
 		new = old;
 		new.k = 1;
@@ -288,8 +283,7 @@ static void ipte_unlock_siif(struct kvm_vcpu *vcpu)
 
 	ic = &vcpu->kvm->arch.sca->ipte_control;
 	do {
-		old = *ic;
-		barrier();
+		old = READ_ONCE(*ic);
 		new = old;
 		new.kh--;
 		if (!new.kh)
-- 
1.9.3

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